Implement support for passing custom text resolution for starting log… (

#4698)

Co-authored-by: Frazer Smith <frazer.dev@outlook.com>

docs/Reference/Server.md

@@ -916,9 +916,25 @@ fastify.ready().then(() => {
 
 Starts the server and internally waits for the `.ready()` event. The signature
 is `.listen([options][, callback])`. Both the `options` object and the
-`callback` parameters follow the [Node.js
-core](https://nodejs.org/api/net.html#serverlistenoptions-callback) parameter
-definitions.
+`callback` parameters extend the [Node.js
+core](https://nodejs.org/api/net.html#serverlistenoptions-callback) options
+object. Thus, all core options are available with the following additional 
+Fastify specific options:
+
+### `listenTextResolver`
+<a id="listen-text-resolver"></a>
+
+Set an optional resolver for the text to log after server has been successfully
+started.
+It is possible to override the default `Server listening at [address]` log 
+entry using this option.
+
+```js
+server.listen({ 
+  port: 9080, 
+  listenTextResolver: (address) => { return `Prometheus metrics server is listening at ${address}` } 
+})
+```
 
 By default, the server will listen on the address(es) resolved by `localhost`
 when no specific host is provided. If listening on any available interface is

lib/server.js

@@ -15,6 +15,10 @@ const {
 module.exports.createServer = createServer
 module.exports.compileValidateHTTPVersion = compileValidateHTTPVersion
 
+function defaultResolveServerListeningText (address) {
+  return `Server listening at ${address}`
+}
+
 function createServer (options, httpHandler) {
   const server = getServerInstance(options, httpHandler)
 
@@ -166,7 +170,7 @@ function listenCallback (server, listenOptions) {
   const wrap = (err) => {
     server.removeListener('error', wrap)
     if (!err) {
-      const address = logServerAddress.call(this, server)
+      const address = logServerAddress.call(this, server, listenOptions.listenTextResolver || defaultResolveServerListeningText)
       listenOptions.cb(null, address)
     } else {
       this[kState].listening = false
@@ -209,7 +213,7 @@ function listenPromise (server, listenOptions) {
     const listen = new Promise((resolve, reject) => {
       server.listen(listenOptions, () => {
         server.removeListener('error', errEventHandler)
-        resolve(logServerAddress.call(this, server))
+        resolve(logServerAddress.call(this, server, listenOptions.listenTextResolver || defaultResolveServerListeningText))
       })
       // we set it afterwards because listen can throw
       this[kState].listening = true
@@ -339,7 +343,7 @@ function normalizePort (firstArg) {
   return port >= 0 && !Number.isNaN(port) && Number.isInteger(port) ? port : 0
 }
 
-function logServerAddress (server) {
+function logServerAddress (server, listenTextResolver) {
   let address = server.address()
   const isUnixSocket = typeof address === 'string'
   /* istanbul ignore next */
@@ -353,7 +357,8 @@ function logServerAddress (server) {
   /* istanbul ignore next */
   address = (isUnixSocket ? '' : ('http' + (this[kOptions].https ? 's' : '') + '://')) + address
 
-  this.log.info('Server listening at ' + address)
+  const serverListeningText = listenTextResolver(address)
+  this.log.info(serverListeningText)
   return address
 }
 

test/server.test.js

@@ -34,6 +34,16 @@ test('listen should accept stringified number port', t => {
   })
 })
 
+test('listen should accept log text resolution function', t => {
+  t.plan(1)
+
+  const fastify = Fastify()
+  t.teardown(fastify.close.bind(fastify))
+  fastify.listen({ port: '1234', listenTextResolver: () => 'hardcoded text' }, (err) => {
+    t.error(err)
+  })
+})
+
 test('listen should reject string port', async (t) => {
   t.plan(2)
   const fastify = Fastify()

test/types/instance.test-d.ts

@@ -217,13 +217,15 @@ expectDeprecated(server.listen('3000', ''))
 // test listen opts objects
 expectAssignable<PromiseLike<string>>(server.listen())
 expectAssignable<PromiseLike<string>>(server.listen({ port: 3000 }))
+expectAssignable<PromiseLike<string>>(server.listen({ port: 3000, listenTextResolver: (address) => { return `address: ${address}` } }))
 expectAssignable<PromiseLike<string>>(server.listen({ port: 3000, host: '0.0.0.0' }))
 expectAssignable<PromiseLike<string>>(server.listen({ port: 3000, host: '0.0.0.0', backlog: 42 }))
 expectAssignable<PromiseLike<string>>(server.listen({ port: 3000, host: '0.0.0.0', backlog: 42, exclusive: true }))
 expectAssignable<PromiseLike<string>>(server.listen({ port: 3000, host: '::/0', ipv6Only: true }))
 
 expectAssignable<void>(server.listen(() => {}))
 expectAssignable<void>(server.listen({ port: 3000 }, () => {}))
+expectAssignable<void>(server.listen({ port: 3000, listenTextResolver: (address) => { return `address: ${address}` } }, () => {}))
 expectAssignable<void>(server.listen({ port: 3000, host: '0.0.0.0' }, () => {}))
 expectAssignable<void>(server.listen({ port: 3000, host: '0.0.0.0', backlog: 42 }, () => {}))
 expectAssignable<void>(server.listen({ port: 3000, host: '0.0.0.0', backlog: 42, exclusive: true }, () => {}))

types/instance.d.ts

@@ -74,6 +74,12 @@ export interface FastifyListenOptions {
    * @since This option is available only in Node.js v15.6.0 and greater
    */
   signal?: AbortSignal;
+
+  /**
+   * Function that resolves text to log after server has been successfully started
+   * @param address
+   */
+  listenTextResolver?: (address: string) => string;
 }
 
 type NotInInterface<Key, _Interface> = Key extends keyof _Interface ? never : Key